Narrator: Smoking at work can be dangerous -- even if you don't smoke. This is Science Today. Katherine Hammond, an environmental health researcher at the University of California, Berkeley, measured levels of second-hand cigarette smoke at 25 different workplaces, comparing places that banned smoking with those that restricted it to one room, and comparing both of those with places that had no restrictions.

Hammond: Workplaces which banned smoking have much much lower levels than those than restrict it. And those levels are in fact much much lower than places that allow smoking. In places that allow smoking, we found a significant number of people can be exposed to what's a truly dangerous-to-their-health level of passive smoking.

Narrator: Hammond compared their exposure to that suffered by non-smokers who live with smokers.

Hammond: And what we found is that the workplace exposure during the time you're at work can actually be higher in many cases than in people's homes. It's not by choice -- and yet they're being exposed to levels which have been now shown to cause adverse health effects.

Narrator: For Science Today, I'm Steve Tokar.